1. Field of the Invention
This invention relates generally to a DC power source apparatus and a control apparatus thereof and more particularly to a DC power source apparatus and a control apparatus thereof to supply a DC load a controlled DC power obtained from an AC power source through a current regulator including electronic contactors and a rectifier circuit.
2. Description of the Prior Art
As an example of DC power source apparatus, FIG. 1 shows a circuitry for a conventional DC-type welder 40. In FIG. 1, from an AC power source 1, conduction-phase-controlled AC current Iac is supplied through a current regulator 2 including electronic contactors such as antiparallel-connected thyristors 2a and 2b to a primary winding of a transformer 3. To a secondary winding of the transformer 3, a rectifier circuit 4 including bridge-connected diodes 4a, 4b, 4c and 4d is connected, and a DC current Idc which is a rectified output of the transformer 3 is supplied to a DC load such as welder electrodes 5.
DC current which flows through the welder electrode 5 is detected by a current detector 6, and this detected signal is amplified and averaged by an amplifier 7. The output of the amplifier 7 is compared with a predetermined current reference I.sub.R at an adder 7-1, and the compared result difference is supplied through an amplifier 8 to a phase controller 9. The phase controller 9 controls conduction phase of the thyristors 2a and 2b of the current regulator 2 by firing pulse Vg so that such difference becomes zero, namely the DC current Idc which flows through the electrodes 5 becomes equal to the current reference I.sub.R.
The above-described conventional DC power source apparatus has disadvantages:
(1) Since a welding DC current is generally large as in the range of from approximately 5 to 30 KA, the current detector thereof has difficulties to be inserted in place, or becomes larger in dimension, thus economical drawbacks have been experienced.
(2) The distance between the installation site of the control apparatus which incorporates a current control circuit and electronic contactors and that of the welder main unit which incorporates a transformer and a rectifier circuit has frequently become as far as several dekameters. (This derives from such a necessity that the secondary winding of transformer through which such a current of several deca-KA flows should be minimal in wiring length.) Therefore, the conventional apparatus which detects current at the DC side has inevitably had a lengthy wiring distance between the welder main unit and the control apparatus thereof, and this causes troubles such as noise disturbances, and also increases in cost of the installation.